Objective To study the diffusion behavior of gas in poly( vinylidene fluoride) ( PVDF) sheet material. Methods The diffusion behavior of oxygen in this sheet material was studied by molecular dynamics simulation method and the diffusion coefficient of oxygen in PVDF sheets was obtained, meanwhile, the effects of time, polymerization degree, temperature and residual pressure on the diffusion coefficient were also discussed. Results Short period of simulation time was unfavorable for the simulation results, and it should be more than 1000 fs. When the degree of polymerization increased from 400 to 800, the diffusion coefficient of oxygen in PVDF declined correspondingly from 4. 77 X10^-6( cm²·s^-1) to 1. 78 X10^-6( cm²·s^-1); when the temperature was elevated from 198 K to 303 K, the diffusion coefficient increased from 1. 06 X 10^-6( cm²·s^-1)to 1. 42X10^-6( cm²·s^-1)and when the residual pressure varied from 60 kPa to 100 kPa, the diffusion coefficient declined from 7. 07 X10^-6( cm²·s^-1)to 3. 06 X10^-6( cm²·s^-1). Conclusion The diffusion coefficient of oxygen in PVDF declined with the increase of polymerization degree and residual pressure, while increased with the increase of temperature.